Slow Blow pre?

[KrIVIUM2323]

huge trx on left corner...

This is not a 1577. In the picture the big lundahl on the left is the choke for psu (10h 200ma: LL1673 10H) and the other transformer is the power transformer. The 1577 is approximately same size as 1538.
On the schematic linked on the site you give there's a typo (as on many versions of the slowblow schematics). Take a look at the original VSplanet thread i think Sysmofit explained that.

 

[kambo]

although i have a working unit now, i was well confused,
all that makes sense now 

 

[kambo]

i have hum problem, i have been trying to figure out... 
-80db hum is at 100hz and its harmonics... i think i should do better than this,..

when i kill power, hum dies too, so its not fading away slowly;
is this mean my layout ?
or heater supply ?
or B+ ?

 

[FotisGR]

maybe ground loops...maybe transformer's interference ?
i have build this project many times with no problem at all... is quiet like death ... and sounds like an orgasm

 

[kambo]

i am suspecting B+ filter caps... more i add, less hum i get...
besides that, sound is more than an orgasm  ;D

 

[FotisGR]

can you post some high resolution pictures for help? this pre is without hum even with 30-40uf capacitance...with some pictures may we help you...

 

[kambo]

high res there,
https://www.yousendit.com/download/MzZFUGhWT01iV3hjR0E9PQ

schematic 12au7 double prpp version...

i have 1uf solen fast's under Electrolytic caps ...

my heater caps are only 3x1000uf ?
heater supply 12V DC, connected to pin 4-5, leftout pins from heaters (8 and 9 depend on tube)  un_connected
tried 6.3 heater (4-5 8 and 9) too, no change...


i used regulated B+ no change on hum,
changed tubes, no change...

i tried all sort of grounding, including two resistors from  heaters to make center_tap to B+ connection as shown on one slowblow PSU...
no change.. played with cables, no change... cables are only sensitive to noise, not hum...

ripple is 0.005V on B+,
0.006V on heaters

i will draw/send my layout later today...

 

[kambo]

.

 

[kambo]

aaaaaaggggrrrrr
i cant believe i made the same mistake again... i mixed pin 6 and 7 on 5687... 
;D

all sorted now

i discovered it while i was copying my exact layout for you to go thorough, and boom, there we go  ;D
i did checked the layout many times, but didnt see that mistake until i started to draw it for you...
many thanks FotisGR,

 

[millzners]

aaaaaaggggrrrrr
i cant believe i made the same mistake again... i mixed pin 6 and 7 on 5687...   
;D

all sorted now

i discovered it while i was copying my exact layout for you to go thorough, and boom, there we go  ;D
i did checked the layout many times, but didnt see that mistake until i started to draw it for you...
many thanks FotisGR,

If it makes you feel any better, I had never heard of this design until your post moved this thread up to the top of the heap.  Now that I've looked into it a bit, I'm intrigued...  I might go for one.  How do you like yours?

 

[kambo]

aaaaaaggggrrrrr
i cant believe i made the same mistake again... i mixed pin 6 and 7 on 5687...   
;D

all sorted now

i discovered it while i was copying my exact layout for you to go thorough, and boom, there we go  ;D
i did checked the layout many times, but didnt see that mistake until i started to draw it for you...
many thanks FotisGR,

If it makes you feel any better, I had never heard of this design until your post moved this thread up to the top of the heap.  Now that I've looked into it a bit, I'm intrigued...  I might go for one.  How do you like yours?

FotisGR says it all  ;D

and sounds like an orgasm

 

[kambo]

my hum is down to -90db at 100hz, near max gain,,,
lower the gain lower the hum, way below -100db at usable gain settings

noise: what noise  ;D, its damn silent  ;D

would hum get better, if spent more time with layout?
i still have some crocodile wires going around,,,,

test:
20db pad,
600ohm output att,
min gain, med gain, max gain, settings
output level controlled with 600ohm att for RMAA
input lundahl 1538, output lundahl 5402, tubes, 6sn7, 5687
lynx aurora, RMAA pro (asio)


EDIT : heaters ripple  (6.3vdc): 0.003V

 

[kambo]

my slowBlow is back home, and i am building a new one here.
can i use 12uf for the output cap instead 10uf, what difference would it make ?

 

[Kingston]

"no difference"

you will see some changes at or below 10-20hz depending on the transformer resonance bump. 1dB here and there so close to DC on a tube amp, we just don't care.

 

[kambo]

cool


update to my February 18, 2011 post :

my finished unit back home is orgasmic as described here btw. 

 

[kambo]

finally finished another one, with more knowledge this time. thanks to every one.

here is a freq response  U47fet + slowblow, max and 9 o'clock min gain settings...
220 ohm resistor connected response is pretty much the same...

edit: this to show only noise, not frequency response... its damn quiet mic pre... 

 

[kambo]

here is a working two channel slow blow 6sn7-5687 version.
series wired heaters at 12.4 VDC, filtered, not regulated.
B+ is 350_ish
sounds great, and quiet.

 

[kambo]

this is the PSU for B+,

resistor is 1K 5w actually...
i am working on phantom, B+, and heater all in one psu...
only two of those large caps are in use for both channel... (470uf/500v)
no choke either... i dont know if this pre would sound any better with choke in B+ supply ?

 

[buildafriend]

this is the PSU for B+,

resistor is 1K 5w actually...
i am working on phantom, B+, and heater all in one psu...
only two of those large caps are in use for both channel... (470uf/500v)
no choke either... i dont know if this pre would sound any better with choke in B+ supply ?

Those caps are nice and large. I'm curious how my trifecta of 22uF will hold its ground compared to your duo of 470uF

I was also curious of the sonic impact of the choke.

 

[kambo]

both versions of the slowblow schematics work the way they are without any mod or additional resistors!
output cap is 10uf, may be typo on ur post for 1 -one-uf
not the same exact design but, check Ian's Classic Solo preamp notes, and its PSU...
some nice educational notes (SRPP, mu follower, PSU etc)
i have a habit of using LL5402 2:1 on output for pretty much everything....
and it always sounds great...
tried choke on PSU, i didnt hear/measure any noticeable difference!